Flanged fittings are used for a variety of purposes in rigid piping systems. For example, in hot tapping operations a fitting can be welded to the pipeline at a location where the tap is to be made. The fitting can extend radially from the pipeline. After the fitting with flange is attached, a tapping valve can be attached to the flange and a tapping machine can then be mounted on the tapping valve. After the tapping operation is complete, the tapping machine can be removed from the tapping valve and replaced with a plugging machine to provide a non-permanent plug which blocks flow of material being transported through the pipeline so that maintenance can be performed on the pipeline. Following maintenance, the non-permanent plug can be withdrawn from the pipeline and replaced with a permanent plug which is positioned in the fitting. To complete the operation, a blind flange is connected to the flanged fitting on the pipeline.
Flanged fittings may also be used in line stop assemblies in operations where it is desired to temporarily prevent fluid flow through a selected pipeline section, such as to provide maintenance or modifications a downstream pipeline section. In a line stop assembly a pipeline sleeve can be first mounted or clamped over a target segment of the pipeline. A flanged fitting can be attached to the pipeline through the pipeline sleeve to extend radially from the pipeline. Next, a temporary valve can be attached to the flanged fitting and the pipeline can be tapped. After the tapping process, a completion plug can be secured in the flanged fitting, the temporary valve can be removed, and a blind flange connected to the flanged fitting.
Many flanged fittings have a “T” shape with a circular flange portion, a tubular neck portion with a distal end that can be attached to a pipeline, and a central bore extending through the flange and neck portions. Depending on the mode of attachment of the flange to the pipeline, it may be desired to modify the flange, such as by welding additional metal pieces to the neck of the fitting. However, such constructions may not be suitable for use in pipeline operations as the modifications may result in structural problems and cause the fitting to fail.